1. Field of the Invention
The present invention relates to a thermosetting polyimide resin composition which is useful in the fields of various heat-resistant coating materials and electrical insulating materials, for example, layer insulating materials of printed circuit boards, build-up materials, insulating materials of semiconductors, and heat-resistant adhesives, and a process for producing a polyimide resin, which is applicable for the thermosetting polyimide resin composition.
2. Description of Related Art
It has recently been required to improve heat resistance and electrical characteristics of resins in various fields, particularly in the electrical and electronics industries. As a resin composition having improved heat resistance, there is known a polyimideamide resin composition comprising a polyamideimide resin obtained by synthesizing an isocyanurate ring-containing polyisocyanate, an aromatic isocyanate and a polycarboxylic acid containing lactam and an acid anhydride in a cresol solvent, and an epoxy resin (see, for example, Japanese Patent Unexamined Application, First Publication No. Sho 55-137161 (pages 2-5)).
Also, there is known a process for producing a polyimide resin which is soluble in a general-purpose solvent, for example, aprotic polar organic solvent such as ketone solvent, ester solvent or ether solvent, excluding a solvent having strong odor and strong toxicity such as cresol, for example, a polyimide resin obtained by reacting an aliphatic isocyanate compound and/or an alicyclic isocyanate compound, which have two or more isocyanate groups in the molecule, with a tricarboxylic anhydride and/or a tetracarboxylic anhydride, and a polyimide resin composition comprising the polyimide resin and the epoxy resin (see, for example, Japanese Unexamined Patent Application, First Publication No. 2001-316469 (pages 3-9).
However, cured articles obtained by curing the polyimide resin composition comprising a polyimide resin and an epoxy resin described in Japanese Unexamined Patent Application, First Publication No. Sho 55-137161 and Japanese Unexamined Patent Application, First Publication No. 2001-316469 are superior in heat resistance, but have high dielectric constant and high dielectric loss tangent and are also inferior in mechanical properties such as tensile strength and tensile elongation, and thus the cured articles are hard and brittle.